The transmission of messages in communications systems is subject to timeouts, i.e. each message is required to be sent during a specified time interval. Timeouts are based on the time interval starting from the last octet of a requested message sent to the last octet of a response message received. Different timeouts are specified according to the priority of the messages. The priority of the message is determined according to the time sensibility on the transmission of the message. An example of such a protocol with up to 3 priorities is specified in the Recommendation ITU-T G.992.3. This protocol defines timeouts of 400, 800, and 1000 ms for priorities 1, 2, and 3 respectively. Messages with lower priority value have precedence over messages with higher priority value, e.g. a message with priority 1 has precedence over a message with priority 2 and a message with priority 2 has priority over a message with priority 3.
However this protocol does not permit to transmit messages requiring a transmission time which is longer than the timeout or to transmit messages which are longer than the maximal packet size. This problem has also been discussed in the Contribution DC-023 presented to the ITU-Telecommunication Standardization Sector, Study Group 15.
What is needed therefore is to provide a message protocol that allows long messages to be transmitted in communications systems wherein message durations and/or message lengths are restricted.